Volute with two chambers for a gas turbine

ABSTRACT

A volute ( 10 ) with two chambers for a gas turbine ( 50 ), including a circumferential conduit ( 11 ) in the form of a spiral, a first opening ( 12 ) oriented tangentially to the said circumferential conduit ( 11 ), toward the outside of the said circumferential conduit ( 11 ), and a second circumferential opening ( 13 ) located at the center of the said circumferential conduit ( 11 ). A wall ( 15 ) separates the said circumferential conduit ( 11 ) into two symmetrical chambers ( 18 ) ( 19 ), with a first fluid and a second fluid being able to circulate independently and in an isolated manner between the said first opening ( 12 ) and the said second opening ( 13 ). The said first opening ( 12 ) allows a linear flow of the two fluids between the said circumferential conduit ( 11 ) and a chamber exterior to the said circumferential conduit ( 11 ), while the said second opening ( 13 ) allows a radial flow of the said two fluids between the said circumferential conduit ( 11 ) and a chamber interior to the said circumferential conduit ( 11 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to French patent application No. FR 13 01004 filed on Apr. 30, 2013, the disclosure of which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The subject area of the present invention is gas turbines. The invention relates to a volute with two chambers. This volute with two chambers is intended particularly for a gas turbine, in order to guide the incoming air between the gas turbine and a heat exchanger. The invention also relates to a gas turbine equipped with this volute with two chambers, as well as a rotary-wing aircraft powered by one or more of these gas turbines.

(2) Description of Related Art

It is known that the efficiency of gas turbines is relatively low. Particularly for turboshaft engines (a specific type of gas turbine used traditionally for helicopters), this efficiency is on the order of 25%.

One known solution for improving this efficiency is to heat the air, doing so after compression and before its entry into the combustion chamber of the gas turbine. This makes it possible to reduce thermal loading in the combustion chamber, and thereby to reduce the fuel consumption of this gas turbine.

This heating of the incoming air may be achieved, in particular, by using the heat of the exhaust gases leaving the combustion chamber, inasmuch as this heat generally is not used. Customized heat exchangers are used for this purpose, particularly in industrial thermal power plants.

Conversely, the use of such exchangers in the specific area of rotary-wing aircraft and helicopters in particular, encounters several major problems, such as the mass and volume of these exchanges, as well as a loss of power by the gas turbine using such a heat exchanger.

On the one hand, the exhaust gases leave the combustion chamber of a gas turbine at high speed, and the circulation in a heat exchanger that recovers part of their heat generates substantial pressure losses for these exhaust gases, thereby entailing a loss of power by the gas turbine.

On the other hand, the passage of the compressed air leaving the compressor through the exchanger before being injected into the combustion chamber also generates substantial pressure losses for this compressed air, thereby reducing the performance of the gas turbine.

Furthermore, because the space available in a helicopter is limited, the installation of a heat exchanger in a gas turbine poses space problems. Last, the additional mass resulting from the incorporation of such a heat exchanger is also an important criterion that affects the performance of the helicopter.

It is known that U.S. Pat. No. 5,182,904 describes a gas turbine whose exhaust gases can be directed, by means of a system of circular valves, toward a first or a second flow, depending on the desired power to be generated by this gas turbine. According to the first flow, the exhaust gases drive several turbocompressors that compress the ambient air before directing it toward a centrifugal flow compressor. According to the second flow, the exhaust gases are directed toward heat exchangers, in order to heat the compressed air leaving the centrifugal flow compressor before the gases are injected into the combustion chamber. A circumferential duct directs the compressed air from the outlet of each heat exchanger to the combustion chamber, with the heat exchangers and the compressor is being positioned in parallel with the centrifugal flow compressor and the combustion chamber.

Furthermore, European patent No. EP 1,621,742 discloses a gas turbine that includes an annular heat exchanger positioned in series with this gas turbine—more specifically, in the exhaust pipe. Two axial ducts direct the compressed incoming air from a circumferential collector of the compressor toward the heat exchanger, while two other axial ducts direct the compressed and heated incoming air from the heat exchanger to a circumferential diffuser for the combustion chamber. Nevertheless, the pressure losses are substantial, especially in the passages between the ducts and the collector and the diffuser, respectively, as well as between the ducts and the heat exchanger, inasmuch as the flow of compressed incoming air must follow a bend whose angle is on the order of 90°.

It is also known that U.S. Pat. No. 2,801,043 describes a compressor equipped with a circumferential duct that includes two chambers that are separated by a partition that serves as a thermal insulator. The circumferential duct includes a radial opening at its center and two diametrically opposed tangential openings, with each chamber including one tangential opening.

Furthermore, German patent No. DE 19653057 describes a circumferential duct that supplies air to a turbine. This circumferential duct includes an outlet at its center and a tangential inlet that is divided into four air inlets. Air can circulate in chambers that are isolated at the tangential inlet and are recombined at the central outlet.

Moreover, British patent No. GB 563,918 and Swiss patent No. 248,924 describe a heat machine whose compressor and turbine are contiguous, thereby forming a circumferential duct equipped with two independent chambers that are separated by a partition. A central opening in this duct also includes a separation, in order to be shared by the two chambers. Compressed air enters a first chamber through the central opening and is then directed to a combustion chamber. Burned gases then enter the second chamber and leave through the central opening.

Last, U.S. patent publication No. 2009/0282804 describes a gas turbine that includes an annular heat exchanger located in parallel with this gas turbine—more specifically, around the combustion chamber. This heat exchanger includes three different flows, with two flows directing the compressed air from the compressor to the combustion chamber and with one exhaust-gas flow allowing this compressed air to be heated. Because the heat exchanger is installed around the combustion chamber, this gas turbine is relatively compact. Conversely, the flows of compressed air and of exhaust gas undergo substantial pressure losses when entering and leaving this heat exchanger.

Thus, solutions exist for the use of heat exchangers in order to improve the efficiency of a gas turbine.

However, the use of such a heat exchanger entails substantial pressure losses, not only for the incoming compressed air but also for the exhaust gases. These pressure losses lead to a loss of power by the gas turbine and may be harmful, particularly during certain flight regimes, such as takeoff, landing, and (for rotary-wing aircraft) stationary flight.

BRIEF SUMMARY OF THE INVENTION

Thus, the goal of the present invention is to propose a circumferential volute for a gas turbine that makes it possible, in particular, to limit the pressure losses of the compressed incoming air.

The term “volute” is understood as referring to a duct that is in the form of a coil or spiral.

According to the invention, a volute with two chambers for a gas turbine includes a circumferential conduit in the form of a spiral and two openings. A first opening is oriented tangentially to this circumferential conduit, toward the outside of this circumferential conduit, while a second circumferential opening is located at the center of this circumferential conduit.

Thanks to this spiral form of the circumferential conduit, a fluid circulating in this volute with two chambers closed tangentially to this circumferential conduit. Conversely, this fluid has a linear flow upon passing through the first opening between the circumferential conduit and a chamber exterior to this circumferential conduit, whereas this fluid has a radial flow upon passing through the second circumferential opening between this circumferential conduit and a chamber interior to this circumferential conduit.

This volute with two chambers is notable in that it includes a wall separating the circumferential conduit into two separate chambers. Thus, a first fluid and a second fluid can circulate independently and in an isolated manner between the first opening and the second opening.

If, in particular, the two fluids circulating respectively in each chamber of this circumferential conduit are at the same pressure, then the pressure of the two fluids on either side of this wall will be balanced. Indeed, this wall performs little mechanical work, and is subjected only to slight stresses. Consequently, the mechanical characteristics of this wall may be slight, and this wall may be thin.

Advantageously, this thin wall also allows a thermal exchange between the first fluid and the second fluid circulating respectively in the two chambers of the circumferential conduit. Furthermore, because the pressure difference between the two fluids is slight, the thickness of this wall can be reduced.

For example, the circumferential conduit may be 0.8 mm (0.8 millimeter) thick, whereas the wall may be between 0.4 and 0.8 mm thick, with this wall and the circumferential conduit being made of stainless steel or Inconel.®

Thus, this volute with two chambers may replace two independent conduits that are used in the traditional manner, thereby reducing the mass and the space requirement of such a device. Furthermore, this single volute with two chambers is easier to install than two independent conduits.

Advantageously, the spiral form of the circumferential conduit allows a linear flow of a fluid entering through the first opening in this circumferential conduit to be converted into a tangential flow, while limiting the pressure losses of this fluid that might occur during such a conversion. Similarly, this spiral form of the circumferential conduit allows a radial flow of a fluid entering through the second opening in this circumferential conduit to be converted into a tangential flow, while limiting the pressure losses of this fluid. Such an advantage is also provided for a fluid exiting through the first opening or through the second opening, with this spiral form making it possible to convert a tangential flow of this fluid in the circumferential conduit into a linear or radial flow, respectively, while limiting the pressure losses of this fluid.

Furthermore, blades may be provided in the second circumferential opening in order to facilitate the conversion of a radial flow of a fluid entering through the second opening into a tangential flow in the circumferential conduit. Thus, these blades also make it possible to reduce the pressure losses that might occur when a fluid passes through this second opening and when the flow is converted there.

Blades may also be located at the second circumferential opening, in order to facilitate the passage of a flow leaving the circumferential conduit.

Furthermore, the position and the shape of the blades may be different, depending on whether the fluid is entering or leaving through this second opening, in order to optimize the conversion of the flow of this fluid.

Consequently, the pressure losses of the fluids circulating through these two chambers of the volute with two chambers are limited.

Furthermore, these two chambers may be equal or even symmetrical.

Last, the circumferential conduit may be in the form of a water droplet, in order to optimize the flows of the fluids inside the volute with two chambers. This water-droplet shape ensures good distribution of the deformations associated with the pressure of the fluids circulating in each chamber of this circumferential conduit. These deformations are acceptable even with thin metal sheets, when the pressure of the fluids is, for example, on the order of 8 bars. Accordingly, the pressure losses of these fluids circulating in the circumferential conduit are limited.

Conversely, if the circumferential conduit has, for example, sharp edges (as is the case with a conduit having a rectangular cross-section), turbulence may occur in the fluid flows, thereby disrupting these flows and generating concentrations of stresses at these sharp edges. For example, major secondary turbulence areas, with the creation of quasi-stationary vortices, may be created in the corners of such a conduit, with the resulting generation of major pressure losses.

Furthermore, depending on the material used, such a circumferential conduit with a rectangular cross-section and sharp edges may be difficult to implement, and may therefore lead to the use of thicker metal sheets.

The management of leakproofness is another delicate aspect of the integration of the conduits, particularly between the conduits and/or between each conduit and the exterior. Advantageously, the use of a single conduit separated by a wall facilitates this leakproofness. This leakproofness may be achieved, for example, by means of a metal joint or a very good surface condition.

The circumferential conduit preferably consists of two circumferential half-conduits in the form of a spiral that are linked to each other by means of the wall. Two circumferential half-conduits are in fact easier to implement. Furthermore, the wall is also easier to implement between these two circumferential half-conduits. Similarly, leakproofness is easier to achieve between this wall and the two circumferential half-conduits.

In particular, the volute with two chambers according to the invention can be used in a gas turbine. A gas turbine usually includes a compressor (for example, a centrifugal compressor) that compresses the ambient air; a combustion chamber in which a mixture containing this compressed ambient air and a fuel is burned; an expansion turbine that allows the energy contained in the burned gases to be converted into mechanical energy; and an exhaust duct through which the exhaust gases are discharged. This gas turbine may also include a heat exchanger that allows the exhaust gas to heat the compressed air leaving the compressor, prior to injection into the combustion chamber, thereby increasing the efficiency of the gas turbine. This heat exchanger is located between the expansion turbine and the exhaust duct, and includes an inlet conduit and an outlet conduit for the compressed air.

The volute with two chambers according to the invention may then make it possible to link the compressor to the heat exchanger, on the one hand, and the heat exchanger to the combustion chamber, on the other hand, by means of the inlet and outlet conduits. Accordingly, the compressed air leaving the compressor enters a first chamber of the circumferential conduit, doing so through the second opening, and is then directed toward the first opening before entering the inlet conduit of the heat exchanger. Next, the compressed air, having been heated by its passage through the heat exchanger, leaves the outlet conduit of this heat exchanger and enters the second chamber of the circumferential conduit, doing so through the first opening, and is then directed toward the second opening before entering the combustion chamber of the gas turbine.

Thus, the use of this volute with two chambers enables the use of a heat exchanger on the gas turbine, while limiting the pressure losses of the compressed air when the air is carried to this heat exchanger and also when it returns from this heat exchanger to the combustion chamber.

Furthermore, the installation of this volute with two chambers on a gas turbine is easier and requires less space than the use of two independent conduits. Indeed, the compressor outlet and the combustion-chamber inlet of a gas turbine are usually located too close together to allow the installation of two independent conduits. The use of this volute with two chambers makes the gas turbine more compact than it would be if two independent conduits were used.

The mass added by this volute with two chambers is also reduced.

Furthermore, the blades positioned at the second circumferential opening may be located in the circumferential conduit, or else they may preferably be located at the compressor outlet in order to limit the pressure losses during the transition from a radial flow to a tangential flow of the compressed air leaving this compressor.

Blades may also be located in the circumferential conduit, or else at the combustion-chamber inlet, in order to limit the pressure losses during the transition from a tangential flow to a radial flow of the heated compressed air entering the combustion chamber.

These blades may also be located in a circumferential diffuser positioned between the compressor and the circumferential conduit. This circumferential diffuser makes it possible to facilitate the transition between the radial flow of a fluid at the compressor outlet and the tangential flow of this fluid in the circumferential conduit.

The use of this volute with two chambers also enables an exchange of heat between the compressed air leaving the compressor and the heated compressed air during its passage through the heat exchanger, by means of the wall of this volute with two chambers. The efficiency of this heat exchanger is also increased by the countercurrent circulation of the two fluids, namely, when the compressed air leaving the compressor circulates in the first chamber in a direction opposite to the direction of the heated compressed air circulating in the second chamber.

The invention also relates to a gas turbine equipped with such a volute with two chambers.

This gas turbine includes:

A compressor (for example, a centrifugal compressor) that compresses the ambient air;

A combustion chamber in which a mixture containing this compressed ambient air and a fuel is burned;

An expansion turbine that allows the energy contained in the burned gases to be converted into mechanical energy;

An exhaust duct through which the exhaust gases are discharged;

A heat exchanger, located between the expansion turbine and the exhaust duct, that includes an inlet conduit and an outlet conduit for the compressed air, which heat exchanger allows the exhaust gas to heat the compressed air leaving the compressor, prior to injection into the combustion chamber; and

A volute with two chambers, as described hereinabove.

This volute with two chambers links the compressor to the inlet conduit of the heat exchanger, on the one hand, and links the outlet conduit of the heat exchanger to the combustion chamber, on the other hand. Accordingly, the compressed air leaving the compressor enters a first chamber of the circumferential conduit, doing so through the second opening, and is then directed toward the first opening before entering the inlet conduit of the heat exchanger. Next, the compressed air, having been heated by its passage through the heat exchanger, leaves the outlet conduit of this heat exchanger and enters the second chamber of the circumferential conduit, doing so through the first opening, and is then directed toward the second opening before entering the combustion chamber of the gas turbine.

Thus, the use of this volute with two chambers allows the use of the heat exchanger in order to increase the efficiency of the gas turbine by limiting the pressure losses of the compressed air between the heat exchanger and, respectively, the compressor and the combustion chamber.

The use of this volute with two chambers also enables an exchange of heat between the compressed air leaving the compressor and the heated compressed air during its passage through the heat exchanger, by means of the wall of this volute with two chambers.

In particular, such a gas turbine may be used to power a rotary-wing aircraft, such as a helicopter.

Last, the invention also relates to a rotary-wing aircraft that includes at least one gas turbine, as described hereinabove, equipped with a volute with two chambers.

The heat exchanger may also be located at different positions within the gas turbine, with its position having an effect on the volume of this gas turbine.

For example, this heat exchanger may be positioned in series with the compressor, the combustion chamber, and the expansion turbine—that is, within the continuity of these components. In this first case, the gas turbine is longer for an essentially unchanged diameter.

The heat exchanger may also be positioned in parallel with the compressor, the combustion chamber, and the expansion turbine, with an intermediate exhaust duct linking the expansion turbine and this heat exchanger. In the second case, the exhaust gases pass through the intermediate exhaust duct and are directed toward the heat exchanger, which, for example, is then placed next to the compressor, the combustion chamber, and the expansion turbine. This intermediate exhaust duct includes a bend that, because of its customized geometry, makes it possible to ensure that the gases are directed toward the heat exchanger, while minimizing the pressure losses. The gas turbine thus has a more compact volume than in the first case, and can, for example, be incorporated more easily into a helicopter.

The position of this heat exchanger can then be selected in accordance with the volume available for this gas turbine—specifically, in the aircraft in which it is intended to be used.

Although the object of the invention is, among others, to limit the occurrence of pressure losses in the flow of compressed air between the compressor and the combustion chamber, pressure losses nevertheless do occur inside the heat exchanger, particularly in the exhaust gases. These pressure losses then reduce the efficiency of the gas turbine. This pressure loss may be harmful, particularly during certain flight regimes of a rotary-wing aircraft, such as takeoff, landing, and stationary flight, with the power loss directly linked to the pressure losses of the exhaust gases being on the order of 3 to 8%.

The heat exchanger may include a so-called bypass system, which allows the exhaust gases to pass through this heat exchanger while minimizing the pressure losses of these gases. In this operating mode, the heat exchanger does not allow the compressed air to be heated prior to injection into the combustion chamber, but the gas turbine can provide the maximum amount of power to the aircraft for certain specific flight regimes.

Furthermore, in order to provide resistance to the thermal and mechanical stresses while still ensuring the leakproofness necessary for the proper operation of the heat exchanger, metal bellows can be placed between the heat exchanger and the various components of the gas turbine.

In fact, because the heat exchanger is located in a high-temperature environment, all of the components of the heat exchanger and of the gas turbine are subject to expansion. These bellows make it possible to mitigate these expansions. The environment of the heat exchanger is also subject to numerous vibrations. Here again, the bellows allow these vibrations to be absorbed.

In particular, these bellows may be located in proximity to the intermediate exhaust duct between the expansion turbine and the heat exchanger, and also in proximity to the inlet and outlet conduits of the heat exchanger.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention and its advantages will become clear in greater detail within the scope of the following description, which includes examples of embodiments provided for illustrative purposes, with reference to the attached figures, among which:

FIGS. 1 and 2 present a front view and a cross sectional view of a volute with two chambers according to the invention;

FIG. 3 is a front view of a variant of such a volute with two chambers; and

FIGS. 4 and 5 show a gas turbine equipped with a volute with two chambers.

Elements that appear in two or more different figures are indicated by the same reference number.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a front view of a volute (10) with two chambers according to the invention, and FIG. 2 is a cross-sectional view along line A-A of this volute (10) with two chambers.

This volute (10) with two chambers includes a circumferential conduit (11) in the form of a spiral, two openings (12) (13), and a wall (15) separating the said circumferential conduit (11) into two separate chambers (18) (19). A first opening (12) is oriented tangentially to this circumferential conduit (11), toward the outside of this circumferential conduit (11), while a second circumferential opening (13) is located at the center of this circumferential conduit (11). The interior of the circumferential conduit (11), where the second opening (13) is located, may have a cylindrical form, as shown in FIG. 1.

The wall (15) that separates the circumferential conduit (11) into two chambers (18) (19) is shown in FIG. 2, which is a cross-sectional view along line A-A of this volute (10) with two chambers. This wall (15) also separates the first and second openings (12) (13), respectively, into two first openings (12 a) (12 b) and two second openings (13 a) (13 b). Thus, the first chamber (18) has the two openings (12 a) (13 a), while the second chamber (19) has the two openings (12 b) (13 b).

A first fluid can circulate in the first chamber (18) of this volute (10) with two chambers between the two openings (12 a) (13 a), and a second fluid can circulate in the second chamber (19) between the two openings (12 b) (13 b). Thus, the first fluid and the second fluid can circulate independently and in an isolated manner between the two chambers (18) (19), between the first opening (12) and the second opening (13). Furthermore, the wall (15) separating the two fluids advantageously enables an exchange of heat between these two fluids.

Furthermore, the spiral form of the circumferential conduit (11) makes it possible to convert, on the one hand, a linear flow of a fluid entering through the first opening (12) into a tangential flow, and, on the other hand, a radial flow of a fluid entering through the second opening (13) into a tangential flow. Similarly, a tangential flow of a fluid circulating in the circumferential conduit (11) is converted into a linear flow at the first opening (12) and into a radial flow at the second opening (13), respectively. Thanks to this particular spiral form of the circumferential conduit (11), these conversions of the fluid flow take place while limiting the pressure losses of this fluid.

Furthermore, blades (14) may be provided in the second circumferential opening (13) in order to facilitate the conversion of a radial flow of a fluid entering through the second opening (13) into a tangential flow in the circumferential conduit (11). These blades (14) also make it possible to reduce the pressure losses of this fluid. The position and the shape of the blades may be different, depending on whether the fluid is entering or leaving through this second opening (13), in order to optimize the conversion of the flow of this fluid.

These blades (14) may also be located in a circumferential diffuser (16) located at the second opening (13), as shown in FIG. 3. This diffuser (16) facilitates the conversion between the radial flow of a fluid at the second opening (13) and the tangential flow of this fluid in the circumferential conduit (11). This diffuser (16) is located inside the circumferential conduit (11), upstream of the second opening (13), for a fluid entering through the second opening (13).

Furthermore, the two chambers (18) (19), separated by the wall (15), may be equal, or even symmetrical, as shown in FIG. 2.

The material employed in the manufacture of the circumferential conduit (11) and the wall (15) is, for example, but not exclusively, stainless steel or Inconel.®

FIGS. 4 and 5 show a gas turbine (50) equipped with a volute (10) with two chambers according to the invention. This gas turbine (50) may be used, for example, to power a rotary-wing aircraft, such as a helicopter. This gas turbine (50) includes:

A centrifugal compressor (51) that compresses the ambient air;

A combustion chamber (52) in which a mixture containing this compressed ambient air and a fuel is burned;

A diffuser (16) located at the outlet of the compressor (51);

An expansion turbine (53) that allows the energy contained in the burned gases to be converted into mechanical energy;

An intermediate exhaust duct (58), through which the exhaust gases are directed from the expansion turbine (53);

An exhaust duct (55) through which the exhaust gases are discharged;

A heat exchanger (54), located between the intermediate exhaust duct (58) and the exhaust duct (55); and

A volute (10) with two chambers.

This heat exchanger (54) includes an inlet conduit (56) and an outlet conduit (57) for the compressed air. This heat exchanger (54) is positioned in parallel with the compressor (51), the combustion chamber (52), and the expansion turbine (53), with the intermediate exhaust duct (58) linking the expansion turbine (53) and this heat exchanger (54).

The volute (10) with two chambers makes it possible, on the one hand, to link the compressor (51) to the heat exchanger (54) by means of the inlet conduit (56), and, on the other hand, to link the heat exchanger (54) to the combustion chamber (52) by means of the outlet conduit (57). Accordingly, the compressed air leaving the compressor (51) passes through the second opening (13 a), then circulates in the first chamber (18) of the circumferential conduit (11), before being directed, by means of the first opening (12 a) to the inlet conduit (56) of the heat exchanger (54). Next, the compressed air, having been heated by its passage through the heat exchanger (54), leaves the outlet conduit (57) of this heat exchanger (54), then passes through the first opening (12 b) and circulates in the second chamber (19) of the circumferential conduit (11), before being directed, through the second opening (13 b), to the combustion chamber (52).

In this gas turbine (50), the two fluids circulating respectively in the two chambers (18) (19)—that is, the compressed air leaving the compressor (51) and the compressed air heated by the heat exchanger (54)—are at essentially equal pressures. In fact, there is a pressure balance of these two fluids on either side of the wall (15). In fact, this wall (15) does little mechanical work, and therefore may be thin.

For example, this wall (15) is between 0.4 and 0.8 mm thick, whereas the circumferential conduit (11) is 0.8 mm thick.

Consequently, this wall (15) is thin, and allows an efficient exchange of heat between these two fluids. Furthermore, the two fluids circulate in countercurrent in the two chambers (18) (19), with the compressed air leaving the compressor (51) circulating in the first chamber (18) from the second opening (13 a) toward the first opening (12 a), and with the compressed air heated by the heat exchanger (54) circulating in the second chamber (19) from the first opening (12 b) toward the second opening (13 b). The efficiency of this heat exchanger (54) is also increased by this countercurrent circulation of the two fluids.

The use of the volute (10) with two chambers in this gas turbine (50) then makes it possible, on the one hand, to limit the pressure losses of the compressed air when the compressed air is directed to, and returns from, the heat exchanger (54), and, on the other hand, to improve the heating of this compressed air. The efficiency of the gas turbine (50) is then improved through the use of this volute (10) with two chambers in this gas turbine (50).

This volute (10) with two chambers thus replaces two independent conduits in order to supply the heat exchanger (54) with compressed air, thereby generating a reduction in mass as well as in the space requirement. The installation of this volute (10) with two chambers on a gas turbine (50) is also easier than the use of two independent conduits.

Furthermore, blades (14) may be located in proximity to the second opening (13 a) in the circumferential conduit (11), or, preferably, in the diffuser (16).

Similarly, blades (14) may also be used in proximity to the second opening (13 b). These blades (14) are thus located in the circumferential conduit (11) or at the entrance to the combustion chamber (52).

Furthermore, as shown in FIG. 4, the circumferential conduit (11) preferably consists of two circumferential half-conduits (11 a) (11 b), in the form of a spiral, that are linked to each other by means of the wall (15). Two circumferential half-conduits (11 a) (11 b) are in fact easier to implement and to assemble with the wall (15).

Last, in order to provide resistance to the thermal and mechanical stresses while still ensuring the leakproofness necessary for the proper operation of the heat exchanger (54), metal bellows (59) can be placed between the heat exchanger (54) and the volute (10) with two chambers, particularly in the input conduit (56) of the heat exchanger (54).

These metal bellows (59) make it possible to absorb the vibrations and expansions to which the components of the gas turbine—and, in particular, the heat exchanger (54)—are subjected. Such metal bellows may also be located in proximity to the intermediate exhaust duct (58) and the outlet conduit (57) of the heat exchanger (54).

Naturally, the present invention is subject to numerous variants in terms of its implementation. Although several embodiments have been described, it will be readily understood that not all of the possible modes can be identified exhaustively. Any of the means described herein may of course be replaced by equivalent means without departing from the scope of the present invention. 

What is claimed is:
 1. A volute with two chambers for a gas turbine, including: a circumferential conduit in the form of a spiral, a first opening oriented tangentially to the said circumferential conduit, toward the outside of the said circumferential conduit, and a second circumferential opening located at the center of the said circumferential conduit, wherein said volute with two chambers includes a wall separating the said circumferential conduit into two separate chambers, with a first fluid and a second fluid being able to circulate independently and in an isolated manner between the said first opening and the said second opening.
 2. A volute with two chambers according to claim 1, wherein said circumferential conduit is in the form of a water droplet.
 3. A volute with two chambers according to claim 1, wherein said two chambers are equal and symmetrical.
 4. A volute with two chambers according to claim 1, wherein said wall allows a thermal exchange between a first fluid and a second fluid circulating respectively in the said two chambers of the said circumferential conduit.
 5. A volute with two chambers according to claim 1, wherein blades are provided in the said second circumferential opening in order to facilitate the conversion between a radial flow of a fluid in the said second opening and a tangential flow of the said fluid in the said circumferential conduit.
 6. A volute with two chambers according to claim 1, wherein said volute with two chambers includes a diffuser located inside the said circumferential conduit and upstream of the said second opening for a fluid entering through the said second opening.
 7. A volute with two chambers according to claim 6, wherein blades are provided in the said diffuser in order to facilitate the conversion between a radial flow of a fluid in the said second opening and a tangential flow of the said fluid in the said circumferential conduit.
 8. A gas turbine including: a compressor; a combustion chamber; an expansion turbine for burned gases; a heat exchanger allowing exhaust gas to heat compressed air leaving the compressor prior to injection into the combustion chamber, the heat exchanger including an inlet conduit and an outlet conduit for the compressed air; and an exhaust duct; wherein said gas turbine includes a volute with two chambers according to claim 1, with the first opening being linked to the inlet and outlet conduits; with the said second opening being linked to the compressor and to the combustion chamber; with the first chamber being linked to the compressor and to the inlet conduit; and with the second chamber being linked to the outlet conduit and to the combustion chamber.
 9. A gas turbine according to claim 8, wherein said heat exchanger is positioned in series with the said compressor, the said combustion chamber, and the said expansion turbine.
 10. A gas turbine according to claim 8, wherein said heat exchanger is positioned in parallel with the said compressor, the said combustion chamber, and the said expansion turbine.
 11. A rotary-wing aircraft wherein said aircraft includes at least one gas turbine according to claim
 8. 